IL-2 is effective treatment for a significant minority of pts. with melanoma or renal cell cancer. Treatment of other cancers has been much less successful, and treatment of all pts. can be limited by severe systemic toxicity particularly at high doses of IL-2. The encapsulation of IL-2 in liposomes may permit treatment of pts. at currently effective doses with less toxicity, or it may lead to improved efficacy by increasing the dose of IL-2 that can be administered safely. It is also possible that the accumulation of liposomal IL-2 in certain organs will lead to more effective therapy of metastases to these sites. We have initiated a phase Ia/Ib study of liposome-encapsulated IL-2 in pts. with advanced cancer. Liposomal IL-2 is given by 30 min. IV infusion once during week one, three times during week two and five times during week three. Responding pts. are eligible for additional therapy. In addition to response to therapy, pts. are monitored for toxicity and for immunologic changes secondary to treatment. 39 evaluable pts. have been treated at the following dose levels: 1x10/6 u/m2; 3x10/6 u/m2; 4.5x10/6 u/m2, 6x10/6 u/m2; 10x10/6 u/m2; 3x10/7 u/m2, and 5x10/7 u/m2. Dose-limiting toxicity has not been observed. There have been 3 partial responses and two minor responses. Increases in NK activity and serum soluble IL-2 receptor levels have been noted at doses of greater than or equal to 4.5x10/6 u/m2.